Stainproof material and method for manufacturing the same, and coating composition and apparatus thereof

ABSTRACT

Disclosed are antifouling material possessing excellent surface antifouling properties, particularly excellent antifouling activity against greasy stains and soils, a process for producing the same, and a coating composition and an apparatus for the antifouling material. The antifouling material comprises: a substrate; and an inorganic layer consisting essentially of an amorphous metal oxide, the inorganic layer containing an alkali metal and non-bridging oxygen in an amount effective in removing contaminants, derived from an exhaust gas, adhered on the surface of the inorganic layer by cleaning using running water alone to restore the diffuse reflectance of the surface of the inorganic layer to not less than 75% of the initial diffuse reflectance, the inorganic layer constituting the outermost fixed layer of the antifouling material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a material having a surface possessingantifouling activity, particularly excellent antifouling activityagainst greasy stains or soils and a process for producing the same, anda coating composition for the antifouling material and an apparatus forthe production process.

2. Background Art

Conventional methods for making the surface of materials antifoulingcomprises smoothening the surface to physically make it difficult forstains or soils to be deposited on the surface. In other methods,excellent oxidative degradation activity of a photocatalyst fixed ontothe surface is utilized to degrade organic matter or stains or soilsdeposited on the surface are washed away by utilizingsuperhydrophilification of a photocatalyst. In these methods, however,satisfactory antifouling properties may not be enough when greasy stainsor soils are badly deposited or when light is not enough to develop thephotocatalytic activity cannot be obtained.

The following materials are known wherein an inorganic layer is formedon the surface thereof so as to associate with or so as not to associatewith antifouling properties of the surface.

Japanese Patent Laid-Open No.98324/1978 discloses a method whichcomprises coating a colloidal silica-based inorganic coating onto aporous inorganic substrate to form an undercoat, coating an alkalisilicate-based inorganic coating thereon to form a top coat, and thencuring the coatings at room temperature or by heating to impart heatresistance and other properties to the substrate.

Japanese Patent Laid-Open No.123639/1993 discloses a method whichcomprises applying a synthetic resin coating as an undercoat onto thesurface of a porous substrate, such as calcium silicate, applying aninorganic coating as an intermediate coat onto the undercoat, and thenapplying an inorganic coating composed mainly of an alkali metalsilicate onto the surface of the intermediate coat.

Japanese Patent Laid-Open No.278431/1997 discloses a hydrophilic filmwherein the center line average roughness Ra′ on the surface of the filmis 0.5 to 500 nm and the surface is composed mainly of concaves andconvexes with the repetition length of concaves and convexes in planedirection of the surface being not more than 0.5 μm.

Japanese Patent Laid-Open No.227160/1997 discloses a photocatalyticallyhydrophilic member having a layer containing a photocatalytically activetitanium oxide and an amorphous oxide.

Japanese Patent Laid-Open No.9995/1994 discloses a stain or soilremoving method using a water-soluble alkali metal salt. This method ischaracterized in that a soil or stain release agent containing awater-soluble alkali metal silicate is coated onto stains or soilsdeposited onto the surface of the substrate to include the stains orsoils in the soil or stain release agent and, thereafter, the soil orstain release agent containing the stains or soils are removed, thusremoving the stains or soils. Since this soil or stain release agent isnot fixed onto the substrate, the stain or soil removing method ismerely a temporary soil or stain removing method like that using asurfactant-containing detergent.

None of the above prior art methods, however, disclose that theincorporation of satisfactory amounts of an alkali metal andnon-bridging oxygen in an amorphous metal oxide can offer excellentantifouling properties and abrasion resistance.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anantifouling material, which, independently of environment, such asindoor or outdoor environment, can semi-permanently exhibit excellentsurface antifouling properties, particularly excellent antifoulingactivity against greasy stains or soils and, in addition, is resistantto abrasion. It is also an object of the present invention to provide aprocess for producing the same, and a coating composition and apparatusfor the antifouling material and the production process.

The present invention has been made with a view to attaining the aboveobject. According to a first aspect of the present invention, there isprovided an antifouling material comprising: a substrate; and aninorganic layer consisting essentially of an amorphous metal oxide, saidinorganic layer containing an alkali metal and non-bridging oxygen in anamount effective to remove contaminants, derived from an exhaust gas,adhered on the surface of the inorganic layer with running water aloneto restore the diffuse reflectance of the surface of the inorganic layerto not less than 75% of the initial diffuse reflectance, said inorganiclayer being fixed as the outermost layer of the antifouling material.

According to a second aspect of the present invention, there is provideda coating composition for the formation of an antifouling inorganiclayer on the surface of a substrate in the production of the antifoulingmaterial, said coating composition comprising: a solvent; and a solute,the solute comprising at least one member selected from the groupconsisting of an alkali silicate, an alkali aluminate, an alkalizirconate, an alkali borate, an alkali phosphate, and an alkaliphosphonate.

According to a third aspect of the present invention, there is provideda process for producing an antifouling material, comprising the stepsof: applying the coating composition onto the surface of a substrate toform a coating; and heating the substrate to fix the coating of thecoating composition as an antifouling inorganic layer on the surface ofthe substrate.

According to a fourth aspect of the present invention, there is providedan apparatus for producing an antifouling material, said apparatuscomprising coating means for applying the coating composition to form acoating onto the surface of a substrate; and heating means for rapidlyheating the substrate to fix the coating of the coating composition asan antifouling inorganic layer onto the surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram showing an inorganic layer according toone embodiment of the present invention;

FIG. 2 is a diagram illustrating one embodiment of the process forproducing an antifouling material according to the present invention,wherein (a) shows the state of an assembly before heat treatment and (b)shows the state of the assembly after heat treatment and wherein a layer2 a of a coating composition coated onto a substrate 1 is heat treatedto form a thin layer 2 b for imparting a multi-function to the substrate1;

FIG. 3 is a diagrams illustrating another embodiment of the process forproducing an antifouling material according to the present invention,wherein (a) shows the state of an assembly before heat treatment and (b)shows the state of the assembly after heat treatment and wherein, uponrapid heating of a layer 2 a of a coating composition coated on thesubstrate 1 and a layer 4 a, the layer 2 a is converted to a thin layer2 b for imparting a multi-function to the substrate 1 while the layer 4a is converted to a layer 4 b which has non-bridging oxygen andcontributes to the development of hydrophilicity;

FIG. 4 is a diagram illustrating an embodiment of the apparatus forproducing an antifouling material according to the present invention,which comprises: an apparatus for producing earthenware as a substrate,comprising a forming device 5, a glazing device 6, and a firing device7; the apparatus of the present invention provided continuously from theapparatus for producing the substrate, the apparatus of the presentinvention comprising a coating device 8 for coating a coatingcomposition, a rapid heating device 9, and a cooling device 10; and acarrying device 16 provided so that the substrate can be continuouslycarried through within each of the devices and through between thedevices;

FIG. 5 is a schematic diagram showing the structure of the rapid heatingdevice 9 shown in FIG. 4, wherein the rapid heating device 9 comprises aheating element 21, a heat-resistant material 22 which covers theheating element 21 and forms a heating space, carrying means 16 forholding the substrate 23, to be heated, within the heating space andcarrying the substrate in a direction indicated by an arrow A in thedrawing, a carry-in port 24 for carrying the substrate in the heatingspace, and a carry-out port 25 for carrying out the substrate from theheating space;

FIG. 6 is a diagram showing another embodiment of the apparatusaccording to the present invention, wherein a preheater 11 forpreheating the substrate before coating a coating composition and adrier 12 for drying the substrate coated with the coating compositionare additionally provided;

FIG. 7 is a schematic diagram illustrating the measurement of thecontact angle in water of the inorganic layer according to oneembodiment of the present invention with a salad oil;

FIG. 8 is a graph showing the results of a potassium ion elution test inExample C-1, that is, a test on the elution of potassium ions in tiles,with potassium silicate applied therein, which have been heat treatedrespectively at 150° C., 350° C., and 550° C.; and

FIG. 9 is a diagram showing the results of the measurement of thecontact angle in water of tiles, with potassium silicate appliedthereon, which have been heat treated respectively at 150° C., 350° C.,450° C., 550° C., and 800° C., with a salad oil and the results ofthermogravimetric analysis of potassium silicate in Examples C-2 and C-3and Comparative Example C-1.

DETAILED DESCRIPTION OF THE INVENTION Antifouling Material

The antifouling material according to the present invention comprises: asubstrate; and an inorganic layer as an outermost layer consistingessentially of an amorphous metal oxide. The antifouling materialaccording to the present invention has various functions, for example,hydrophilifying, antifouling, antifogging, and antistatic functions.Better antifouling properties can be provided by synergistic effect ofsome of these functions.

(a) Substrate

Substrates usable in the present invention include metals, inorganicmaterials, organic materials, and composites of these materials.Specific examples thereof include interior materials, exteriormaterials, tiles, sanitary wares, tablewares, calcium silicate board,cement extruded boards and other building materials, ceramic boards,semiconductors and other new ceramics, insulators, glasses, mirrors,woods, and resins. Other applications include exterior of buildings,interior of buildings, sashes, windowpanes, structural members, exteriorand coating of vehicles, exterior of machineries and articles, dustproofcovers and coatings, traffic signs, various display devices, advertisingtowers or poster columns, noise barriers for roads, noise barriers forrail roads, bridges, exterior and coating of guard rails, interiorfacing and coating of tunnels, insulators, cover for solar cells, coversfor solar energy collectors of solar water heaters, vinyl plastichothouses, covers for lighting of vehicles, households, stools, bathtubs, wash basins, lighting equipment, covers for lighting,kitchenwares, tablewares, dishwashers, dishdryers, sinks, cookingranges, kitchen hoods, ventilation fans, and films and the like forapplication on the surface of the above articles.

According to a preferred embodiment of the present invention, use of asubstrate comprising a glazed layer as a surface layer provided on anearthenware body is preferred. The composition range of the surfaceglazed layer is as follows. Specifically, the surface glazed layerpreferably comprises, as amorphous components,

(i) 25 to 90% by weight of a tetravalent metal oxide, such as SiO₂ orTiO₂,

(ii) 0.1 to 30% by weight of a trivalent metal oxide, such as A₂O₃,Fe₂O₃, or B₂O₃,

(iii) 0.1 to 15% by weight of a divalent metal oxide, such as MgO, CaO,ZnO, or BaO,

(iv) 0.1 to 15% by weight of a monovalent metal oxide, such as K₂O,Na₂O, or Li₂O, and

(v) 0.1 to 70% by weight of other components, such as fluorides,phosphorus-containing materials, molybdenum compounds, vanadiumcompounds, antimony compounds, and tungsten compounds, and, crystallinecomponents,

(i) 0.1 to 70% by weight of an opacifier, such as ZrSiO₄ or SnO₂ and

(ii) 0.1 to 10% by weight of a pigment.

(b) Inorganic Layer

The inorganic layer according to the present invention is the outermostlayer consisting essentially of an amorphous metal oxide and contains analkali metal and non-bridging oxygen in an amount large enough todevelop desired antifouling properties.

The antifouling properties of the material according to the presentinvention may be evaluated by an exhaust gas contaminant releasing testusing the surface diffuse reflectance as an index. The materialaccording to the present invention has antifouling properties on a levelsuch that the restoration of the diffuse reflectance is not less than75%, preferably not less than 80%, more preferably not less than 90%.

The exhaust gas contaminant releasing test is carried out as follows. Asample to be evaluated is subjected to the step of depositing acontaminant from an exhaust gas onto the sample and the step of washingthe contaminated sample with running water. Before and after thesesteps, the diffuse reflectance and the change in color difference aremeasured on the surface of the sample to evaluate the antifoulingproperties of the sample. The test procedure will be more specificallydescribed.

At the outset, the initial diffuse reflectance of the surface of thesample is measured. The sample is then placed within a containerconnected directly to an exhaust pipe of a diesel car, and an exhaustgas is introduced into the container. In this case, the exhaust gas isintroduced until the color difference on the surface of the samplereaches about 20 or until the diffuse reflectance reaches not more than55%. Thus, the exhaust gas is forcibly deposited onto the surface of thesample. Next, the tile is washed by running water. The washing withrunning water is carried out by spraying water in an amount of about 400cc/m² against the surface of the tile. For the samples after washing,the diffuse reflectance and the color difference are measured.

The term “diffuse reflectance” used herein refers to the proportion ofthe diffused light to the light incident on the surface of the sampleand indicates the brightness of the color on the surface. The term“color difference” refers to the magnitude of the change in colorexpressed using brightness and chromaticity of the color on the surfaceof the sample. The term “restoration of diffuse reflectance” refers tothe percentage change in diffuse reflectance determined by the followingequation and is used as an index for the restoration of the cleanabilityof the sample by washing.

Restoration (%)=(Diffuse reflectance after washing with waterspray/Initial diffuse reflectance)×100.

According to the present invention, the inorganic layer is in the stateof being fixed as the outermost layer of the antifouling material. Byvirtue of the fixed state, the inorganic layer has abrasion resistance.According to the present invention, the level of the abrasion resistanceis not particularly limited so far as the surface is neitherdeteriorated nor damaged under usual service conditions, and may beproperly determined according to the applications of the antifoulingmaterial. For example, when a good surface state is maintained afterrubbing the surface of the inorganic layer with a hard type eraser 100times while applying a predetermined pressure (for example, 1,000 gf/cm²(9.8×10⁴ Pa)), the abrasion resistance may be regarded as good.

The amorphous metal oxide may be a metal oxide capable of forming athree-dimensional network structure, such as SiO₂, Al₂ ^(O) ₃, ZrO₂,B₂O₃, or P₂O₅, or a combination of these metal oxides. Among them, anamorphous metal oxide composed mainly of SiO₂ is preferred from theviewpoint of film formability and hydrophilicity. Alternatively, thedurability and the abrasion resistance of the surface of the layer maybe further enhanced by using SiO₂ as the main component and, at the sametime, using at least one of Al₂O₃, ZrO₂ and B₂O₃ in combination withSiO₂. In the inorganic layer according to the present invention, thethree-dimensional network structure is properly developed, realizingsatisfactory layer strength and in turn abrasion resistance.

Any of lithium, sodium, potassium, rubidium, cesium, and francium may beused as the alkali metal. They may be used alone or in combination oftwo or more. Among them, potassium, sodium, or lithium has considerablyhigh antifouling activity. These alkali metals are considered to developthe antifouling properties by the so-called builder effect.

The content of the alkali metal in the inorganic layer is not less than10% by weight in terms of oxide based on the composition in the surfaceof the layer. The expression “in terms of oxide” means that the contentof the alkali metal ion in the inorganic layer is calculated in terms ofthe content of the alkali metal oxide. The amount of the alkali metalcan be calculated from the composition of the surface obtained by X-rayphotoelectron spectroscopy (XPS) from the surface portion of theinorganic layer.

FIG. 1 is a conceptual diagram of the inorganic layer according to thepresent invention. As shown in FIG. 1, the inorganic layer according tothe present invention has a two-or three-dimensional network structureof oxide which is satisfactory for developing the abrasion resistance,and the alkali metal and the non-bridging oxygen are present in aportion ranging from the surface of the inorganic layer to the interiorthereof.

The term “non-bridging oxygen” used herein refers to the followingoxygen. In a large part of the coating composition as the material forthe inorganic layer, M—OH (wherein M represents a metal element withspecific examples thereof including silicon, aluminum, zirconium, boron,and phosphorus) is bridged upon heating to form M—O—M bonds. Thisresults in an increase in molecular weight, and this material isstrongly fixed onto the surface of the substrate to develop the abrasionresistance. In this case, a part of the M—OH is incorporated into theresultant polymer molecules and is present as the hydroxyl group (M—OH)without forming the M—O—M bond. A part of this M—OH is ionically bondedto alkali metal ions present in the coating composition to give M—O—X+(wherein×represents an alkali metal) which can be reversibly convertedto M—OH. According to the present invention, these M—OH and M—O—X+ arereferred to as “non-bridging oxygen.”

The non-bridging oxygen has high affinity for water molecules, and evenfunctions to incorporate water molecules in the air into the substratein its surface. Further, upon contact of the surface of the substratewith water, the non-bridging oxygen is likely to be bondedpreferentially to water molecules rather than to molecules which arepresent on the surface of the substrate before water is depositedthereon. This results in the replacement of molecules, which are presentas soils or stains on the surface of the substrate before water isdeposited thereon, with water molecules. Consequently, the molecules,which are present on the surface of the substrate before water isdeposited thereon, are removed from the surface of the substrate. Thus,the presence of the non-bridging oxygen on the surface of the substratecontributes to the development of a very high level of hydrophilicity onthe surface of the substrate. This very high level of hydrophilicityoffers an advantage that not only hydrophilic stains or soils but alsolipophilic stains or soils can be easily washed away with water.

At the same time, the alkali metal on the surface of the inorganic layerrenders greasy stains or soils water-soluble and are partially replacedwith calcium ion or the like contained in water or the like by asubstitution reaction, resulting in the development of builder effect.This is considered to permit stains or soils deposited on the surface ofthe inorganic layer to be more easily removed.

That is, the non-bridging oxygen contributes greatly to thehydrophilicity, and the alkali metal, by virtue of the builder effect,contributes greatly to the cleanability of the surface of the inorganiclayer, and the synergistic effect of them is considered to markedlyimprove the antifouling properties of the surface of the inorganiclayer. The present inventors have further found that the formation ofthe inorganic layer on the glaze layer can significantly enhance theantifouling properties. These suggest that the inorganic layer and theunderlying glaze layer act in some synergistic fashion.

Among the non-bridging oxygens, those ionically bonded to the alkalimetal ion (M—O—X+) can be detected also by photoelectron spectroscopy.However, a simple method may be used wherein an approximate content isdetermined from the amount of the alkali metal eluted upon immersion inwarm water of 50° C. for 24 hr. The percentage elution of the alkalimetal from the inorganic layer upon the immersion in warm water of 50°C. for 24 hr is preferably 0.001 to 80%, more preferably 20 to 80%. Apercentage elution in the above range, even when the amount of M—OH issmall, can provide higher hydrophilicity and in turn better antifoulingproperties because a satisfactory amount of M—O—X+ is present. That is,crosslinking of M—OH can develop M—O—M bonds to ensure the abrasionresistance, and, at the same time, a satisfactory amount of non-bridgingoxygen (M—O—X+) and the alkali metal ion X+ properly present within thenetwork structure can semi-permanently ensure excellent antifoulingproperties.

On the other hand, the amount of hydroxyl groups (M—OH) among thenon-bridging oxygens can be determined by measuring a change in weight,in a temperature region where the weight reduction is created bydehydration between hydroxyl groups, by thermogravimetric analysis (TG).Differential thermal analysis (DTA) may also be used. Further, thehydroxyl group may be detected by infrared spectroscopy or infraredabsorption analysis. The amount of the hydroxyl group among thenon-bridging oxygens may be properly determined so that satisfactoryantifouling properties and abrasion resistance are provided.

Accordingly, the amount of the non-bridging oxygen is preferablydetermined by taking into consideration both the percentage elution ofthe alkali metal and the results of the thermogravimetry (TG).

According to one preferred embodiment of the present invention, thecontact angle in water of the inorganic layer with an oil (for example,oleic acid) is preferably not less than 100 degrees, more preferablymore than 120 degrees. This condition is realized by excellentrolling-up action attributable to the formation of a hydrophilic and oilrepellent fine structure provided as a result of the supply of water inthe inorganic layer. By virtue of this, since combustion products, suchas carbon black or diesel particulates, and powder caused by abrasion oftires are basically hydrophobic, they are less likely to adhere onto thesurface of the inorganic layer.

Further, in the case of an inorganic layer having a contact angle inwater thereof with an oil (for example, oleic acid) of more than 140degrees, independently of the level of load, deposited greasy stains orsoils can be quickly removed by water washing on such a force level aswater spraying wherein the amount of water is small and the force ofwater is small. Therefore, when the contact angle in water of theinorganic layer with an oil is more than 140 degrees, the greasy soil orstain releasing capability of the inorganic layer is better.

According to one preferred embodiment of the present invention, thecontact angle in water of the inorganic layer with an oil (for example,oleic acid) after the immersion in warm water of 50° C. for 6 hr is morethan 120 degrees. In the inorganic layer after the immersion in warmwater of 50° C. for 6 hr, the water-soluble component in the layer issubstantially entirely eluted. Therefore, this state corresponds to thesurface of the inorganic layer after repeated washing. For this reason,in the case of the surface of an inorganic layer having a contact anglein water thereof with an oil of more than 120 degrees, greasy stains orsoils deposited thereon can be simply and repeatedly washed away.

The center line average roughness (Ra) of the surface of the inorganiclayer is preferably Ra<500 nm, more preferably Ra<100 nm. The averageparticle-to-particle spacing (Sm) is preferably 1<Sm<500 nm. This canfurther improve the surface smoothness, and stains or soils are muchless likely to be deposited onto the surface. At the same time,satisfactory fractal effect can be attained, contributing to improvedhydrophilicity and improved oil repellency in the presence of water. Theabove surface smoothness may be realized, for example, by properlyselecting a substrate having a smooth surface. According to the presentinvention, the “center line average roughness or roughness average Ra”means the value obtained by the following formula when sampling themeasurement length L from the roughness curve in the direction of meanline, taking X-axis in the direction of mean line and Y-axis in thedirection of longitudinal magnification of this sampled part and theroughness curve is expressed by Y=f(x):${Ra} = {\frac{1}{l}\quad {\int_{0}^{l}{{{f\quad (x)}}\quad {x}}}}$

In the present invention, the center line average roughness Ra is inaccordance with the definition and designation specified in JIS B0601-1994 and measured with a stylus type surface roughness testeraccording to JIS B 0651-1996. These JIS, together with Englishtranslation thereof, are easily available from Japanese StandardsAssociation (1-24, Akasaka 4-chome, Minato-ku, Tokyo, Japan).

According to a preferred embodiment of the present invention, thethickness of the surface layer is preferably not more than 5 μm, morepreferably 0.01 to 5 μm. This thickness can ensure satisfactorytransparency and can improve the design effect. At the same time, stainsor soils having a penetrating property, such as dyes and Indian inks,are less likely to be absorbed in the layer, resulting in improvedantifouling effect.

According to a preferred embodiment of the present invention, thehalf-value period of electrification on the surface is preferably notmore than 10 sec. In this case, moisture in the air is adsorbed onto thesurface of the inorganic layer, and, thus, electrostatic electrificationis less likely to occur. Therefore, advantageously, the adsorption ofairborne smoke and soot caused by static electricity is less likely tooccur.

According to a preferred embodiment of the present invention, theinorganic layer, when immersed in water at pH 7, has a negative zetapotential. In this case, bacteria or eumycetes and greasy stains orsoils, which are negatively charged in water, are less likely to bedeposited on the surface of the inorganic layer.

According to a preferred embodiment of the present invention, thesurface of the inorganic layer has a pH value of more than 7. When thepH value is on an alkaline side, greasy stains or soils are likely tohave poor affinity for the surface and, thus, the adhesion of the stainsor soils to the surface becomes so low that the greasy stains or soilsare can be more easily washed away by rainfall or the like.

According to a preferred embodiment of the present invention, the heatof wetting by water of the surface of the inorganic layer is at least 1erg/cm² larger than the heat of wetting by water of the tile before theformation of the inorganic layer on the surface of the tile. Thispermits water to be more easily attracted by the surface of theinorganic layer and thus can improve the hydrophilicity and, at the sametime, the oil repellency in the presence of water.

According to a preferred embodiment of the present invention, thesurface layer is transparent. This can maintain the design effect of thesubstrate.

According to a preferred embodiment of the present invention, a metaloxide having photocatalytic activity may be further incorporated intothe inorganic layer to further impart various properties derived fromphotoexcitation, for example, hydrophilicity and bactericidal activity.Suitable photocatalytically active metal oxides include TiO₂.

According to a preferred embodiment of the present invention, anantimicrobial component may be added to the inorganic layer. This canprevent the surface to be soiled with bacteria, mold, or algae. In thiscase, silver, copper, zinc and the like are suitable as theantimicrobial component.

According to one embodiment of the antifouling material according to thepresent invention, a substrate comprising a body having thereon a glazelayer containing a particulate material and/or a transparent thin layermay be used. Such substrates include outdoor tiles and interior tiles.

Particulate materials include, for example, materials having elements,such as silicon, aluminum, iron, titanium, magnesium, calcium,zirconium, zinc, cobalt, manganese, chromium, copper, silver, lead, andnickel. Specific examples thereof include pigment particles, opacifierparticles, and glaze material particles which have remained dissolved ina vitreous component.

Outdoor tiles include exterior tiles, pavement tiles, and interior tilesfor tunnels. The formation of the inorganic layer according to thepresent invention on a tile comprising a body bearing a glaze containingan unmelted particulate material, such as zircon or silica, enablesvarious stains or soils deposited on the exterior to be removed byutilizing the hydrophilic nature of the surface. Further, since thisinorganic layer is oil repellent in the presence of water, it cansuppress the deposition of oil-containing soils or stains such asexhaust gases and smoke and soot in urban areas. Further, since thesurface of the inorganic layer is rendered hydrophilic and oil-repellentin the presence of water or water vapor, the electrostatic adsorption ofairborne smoke and soot onto the surface can be prevented.

Another preferred substrate is an interior tile. The formation of theinorganic layer according to the present invention on a tile comprisinga body bearing a glaze containing an unmelted particulate material, suchas zircon or silica, enables various stains or soils deposited on theinterior to be removed by utilizing the hydrophilic nature of thesurface. Further, since this inorganic layer is oil repellent in thepresence of water, it can suppress the deposition of soils or stainsproduced in kitchens, such as salad oils, and soils or stains producedin bathrooms, such as grime or scale. Furthermore, since the surface ofthe inorganic layer is rendered hydrophilic and oil-repellent in thepresence of water or water vapor, the electrostatic adsorption ofairborne smoke and soot onto the surface can be prevented.

Coating Composition

The coating composition for an inorganic layer according to the presentinvention comprises a solvent and a solute.

The solute is composed mainly of at least one member, as a metal saltwhich upon heating described later can form an amorphous metal oxide,selected from the group consisting of alkali silicates, alkalialuminates, alkali zirconates, alkali borates, alkali phosphates, andalkali phosphonates.

Specific examples of preferred solutes include alkali silicatesrepresented by formula Me₂O.nSiO₂ wherein Me represents an alkali metal,for example, water glass, potassium silicate, lithium silicate, sodiumsilicate, and silica. According to the present invention, the coatingcomposition contains at least one metal selected from the groupconsisting of francium, cesium, rubidium, potassium, sodium, andlithium. Preferred alkali metal silicates include, for example,potassium silicate, sodium silicate, and lithium silicate. When onealkali metal silicate is solely used, lithium silicate exhibits goodgreasy stain or soil releasing properties. Combined use of a pluralityof the alkali metal silicates can improve the water resistance, alkaliresistance, and acid resistance of the inorganic layer. Alkali metalsilicates commercially available in the form of an aqueous solution arealso usable.

The use of an alkali metal silicate can form an inorganic layer havinggood adhesion even at a low temperature of about 150° C. to the surfaceof the substrate. Further, an inorganic layer having high concentrationsof non-bridging oxygen and alkali metal can be formed. This inorganiclayer has excellent greasy stain or soil releasing properties.

The solvent may be one composed mainly of water. The solvent, however,is not particularly limited to this only.

According to a preferred embodiment of the present invention, thecoating composition contains a second component. Specifically, thesecond component is selected from the group consisting of aluminum,titanium, silicon, zirconium, zinc, cerium, tin, antimony, strontium,iron, chromium, phosphorus, boron, cobalt, manganese, copper, silver,platinum, gold, vanadium, tantalum, and bismuth and metal compounds ofthe above metals. Specific examples of metal compounds include SiO₂,SiO₃, Si(OH), Al(OH)₃, TiCl₄, and Ti(OC₃H₇)₄. The addition of the secondcomponent can impart contemplated functions. For example, Al₂O₃, TiO₂and the like, which has high heat of wetting by water, are preferred forimparting hydrophilicity. Cerium capable of causing self-deactivation ofultraviolet light is preferred for ultraviolet absorption. Whenantimicrobial activity is desired, oxides of copper and silver arepreferred. For antifouling against greasy stains or soils, alkali metaloxides are highly effective and thus are preferred. The addition ofphosphorus and boron can advantageously improve the durability ofantifouling materials.

According to a preferred embodiment of the present invention, theconcentration of the alkali metal silicate in the coating composition ispreferably 0.001 to 35% by weight, more preferably 0.001 to 20% byweight, on a solid basis. When the concentration is in the above range,a surface having good properties and good strength can be provided.Further, in this case, it is possible to provide antifouling materialsthe surface of which is even and smooth and has good gloss.

According to the most preferred embodiment of the present invention, thecoating composition basically comprises:

(1) an alkali metal silicate;

(2) a second component; and

(3) a solvent.

According to a preferred embodiment of the present invention, thecoating composition contains a surfactant. The addition of thesurfactant enables the coating composition to be evenly coated.

The average crystallite diameter of the second component is preferablynot more than 100 nm. The upper limit of the average crystallitediameter is preferably about 20 nm, more preferably about 10 nm. Thelower limit of the average crystallite diameter is preferably about 1nm, more preferably about 3 nm. An average crystallite diameter of thesecond component particle in the above range makes it possible toprevent loss of transparency, of a surface with the composition appliedthereto, derived from scattering of visible light caused by theparticles.

Further, the coating composition, upon heat treatment described later,can form an inorganic layer having excellent antifouling properties andabrasion resistance.

Production Process of Antifouling Material

(a) Coating of Coating Composition onto Substrate

According to the process of the present invention, the coatingcomposition is coated onto a substrate. Examples of suitable methods forcoating the coating composition include spray coating, dip coating, flowcoating, spin coating, roll coating, brush coating, and sponge coating.According to a preferred embodiment of the present invention, thecoating composition is coated onto the substrate by spray coating.

According to a preferred embodiment of the present invention, thesubstrate is preheated before coating of the coating composition. Thepreheating of the substrate may be carried out by heating the surface ofthe substrate to 20 to 400° C. The preheating of the substrate isadvantageous in that, upon coating of the coating composition onto thesurface of the preheated substrate, the coating composition evenlyspreads and yields an even coating.

According to a preferred embodiment of the present invention, thesubstrate coated with the coating composition may be dried before heattreatment. Heat treatment described below applies a large heat value tothe substrate. Presence of excess water or solvent component on thesubstrate leads to a fear of the smoothness of the surface of thesubstrate being lost as a result of rapid evaporation of water or thesolvent component and the like due to a rapid temperature change.Therefore, in some cases, preferably, excess water or solvent componentis previously removed by drying. The drying may be carried out by airblasting or heating.

FIG. 2(a) is a schematic diagram showing an assembly comprising a layer2 a of a coating composition coated onto a substrate 1. Upon heattreatment described below, the coating composition layer 2 a is broughtto a thin layer 2 b which functions to impart multi-function to thesubstrate 1. Thus, an antifouling material 3 is obtained.

According to a preferred embodiment of the present invention, thecoating composition may be coated onto the surface of the substrate soas to form a stacked or multi-layered coating. Specifically, anidentical coating composition may be provided and coated on the surfaceof the substrate a plurality of times. Alternatively, a plurality ofdifferent coating compositions may be provided followed by successivecoating of the plurality of different coating compositions onto thesurface of the substrate. The “coating to form a stacked ormulti-layered coating” refers to the so-called “multi-coating” or“recoating.” In this case, an even coating can be realized.

(b) Heat Treatment

The substrate coated with the coating composition is then heat treated.

The heat treatment permits hydroxyl groups (—M—OH (wherein M represents,for example, silicon) in the coating composition to be bridged toproperly develop the three-dimensional network structure of —M—O—M—.This treatment functions to fix an inorganic thin layer having excellentantifouling properties and abrasion resistance onto the substrate.

The heat treatment is preferably carried out by bringing the surface ofthe substrate to 100 to 800° C., more preferably 150 to 600° C., stillmore preferably 150 to 500° C., most preferably 200 to 500° C. The heattreatment temperature, however, is not limited to this only. When theheat treatment temperature is in the above range, the three-dimensionalnetwork structure of —M—O—M— is properly developed to improve thestrength of the inorganic thin layer, thereby imparting excellentabrasion resistance. The presence of a sufficient amount of non-bridgingoxygen M—O—M+ and the presence of a proper amount of an alkali metal ionX+ within the network structure can improve the hydrophilicity and thecleanability, thereby imparting excellent antifouling properties. Thatis, realization of well balanced abrasion resistance and antifoulingproperties can be expected.

The heat treatment time may be properly determined according to the heattreatment temperature, and is not particularly limited. According to apreferred embodiment of the present invention, however, the heattreatment is carried out by “rapid heating.” As used herein, the term“rapid heating” means heating for such a period of time that, althoughheat is evenly spread to the coating composition on the substrate, thetemperature of the whole substrate does not yet reach the temperature ofthe coating on the surface of the substrate. Therefore, preferably, therapid heating is carried out by intensively applying heat to only thesurface of the substrate.

More specifically, the rapid heating time is preferably about 2 to 60sec, more preferably 5 to 60 sec. Rapidly heating the surface of thesubstrate to the above temperature can realize the production of anantifouling material having satisfactory properties with highefficiency. This is particularly because heating to the abovetemperature range results in the formation of non-bridging oxygen withhigh efficiency which is very advantageous from the viewpoint of thedevelopment of hydrophilicity. Further, since the whole substrate doesnot reach the high temperature, breaking or cracking due to heat shockduring temperature rise can be effectively prevented. Further, at thetime of cooling, similar phenomena can be effectively prevented.

According to a preferred embodiment of the present invention, theheating temperature is kept substantially constant during rapid heating.According to a preferred embodiment of the present invention, thetemperature of the atmosphere, in which the substrate is placed duringrapid heating, is preferably 100 to 1000° C., more preferably 200 to1000° C.

According to a preferred embodiment of the present invention, the rapidheating is carried out using heating means of which the heating valueper unit area is not less than 120 MJ/m²·hr, more preferably not lessthan 400 MJ/m²·hr.

The rapidly heated substrate is then cooled to provide a finalantifouling material. According to a preferred embodiment of the presentinvention, the cooling may be rapidly carried out.

According to another preferred embodiment of the present invention,instead of the rapid heating, the heat treatment time may be brought to1 to 60 min. In this case, despite the fact that the temperature isbelow the temperature used in the rapid heating, an inorganic layerhaving excellent antifouling properties and abrasion resistance can beformed. More specifically, the atmosphere temperature is preferably 150to 700° C.

According to one preferred embodiment of the present invention, the heatof immersion on water of the inorganic layer after the heat treatment ispreferably larger than that before the heat treatment. The heat ofimmersion on water include heat of hydration ionic non-bridging oxygen(M—O—X+), hydroxyl group-based non-bridging oxygen (M—OH), and heat ofadsorption derived from hydrogen bonds of water molecules. Incalculating the heat of immersion, it should be noted that, whenreversibly hydratable crosslinkable oxygen atoms are present in theinorganic layer, these oxygen atoms function as hydroxyl groups (M—OH)in the presence of water and thus are regarded as being embraced in thehydroxyl group-based non-bridging oxygen (M—OH). In the case of aninorganic layer wherein the heat of immersion on water of the inorganiclayer after the heat treatment is preferably larger than that before theheat treatment, the hydrophilic and oil repellent nature attributable tothe non-bridging oxygen can be significantly developed, and greasystains or soils deposited on the surface of the inorganic layer can besimply washed away by running water.

According to one preferred embodiment of the present invention, the heatof immersion on water of the inorganic layer is larger than the heat ofimmersion of the inorganic layer on an oil. In this inorganic layer,since the affinity of water for the inorganic layer is larger than theadhesion of the greasy stains or soils to the inorganic layer, supply ofwater permits the inorganic layer to exhibit excellent hydrophilic andoil repellent nature and thus can easily remove the greasy stains orsoils deposited on the inorganic layer.

Apparatus for Producing Antifouling Material

According to the present invention, there is provided an apparatussuitable for producing the antifouling material.

FIG. 4 is an explanatory view of the apparatus for producing anantifouling material according to the present invention. In theapparatus shown in the drawing, the apparatus according to the presentinvention is provided continuously from an apparatus for producing asubstrate. As can be seen from the drawing, the apparatus for producingthe so-called “earthenware” as the substrate comprises a forming device5, a grazing device 6, and a firing device 7. The apparatus according tothe present invention comprises a device 8 for coating a coatingcomposition, a rapid heating device 9, and a cooling region 10. Theapparatus for producing a substrate is provided so as to continue to theapparatus according to the present invention. Further, a carrying device16 is provided so that the substrate can be continuously carried throughwithin each device and between devices. Therefore, the apparatus forproducing a substrate, comprising a substrate forming device 5, aglazing device 6, and a firing device 7 may be properly selected and mayhave other construction according to the substrate to which the processof the present invention is to be applied. The apparatus according tothe present invention is not limited to an apparatus comprising acoating device 8 for coating a coating composition, a rapid heatingdevice 9, and a cooling region 10, and connotes an apparatus, as shownin FIG. 4, which can continuously produce an antifouling material fromthe production of a substrate. That is, a construction, wherein anapparatus comprising a coating device 8 for coating a coatingcomposition, a rapid heating device 9, and a cooling region 10 areprovided just behind (downstream of) the apparatus for producing asubstrate, also falls within the scope of the present invention.

A substrate is formed in the forming device 5 shown in the drawing. Thesubstrate is coated with a glaze by means of the grazing device 6, andthen fired in the firing device 7. The substrate, which has been firedin the firing device 7, has still high temperature. According to apreferred embodiment of the present invention, the coating compositionis coated onto the substrate when the substrate is in the state of acertain high temperature.

The construction of the coating device 8 shown in the drawing may varydepending upon selected coating methods. For example, when spray coatingis selected, the coating device comprises a device for spraying acoating composition.

FIG. 5 is a schematic diagram showing the structure of the rapid heatingdevice 9 shown in FIG. 4. The rapid heating device 9 basically comprisesa heating element 21, a heat-resistant material 22 provided so as tocover the heating element 21 and to form a heating space, carrying means16 for holding a substrate 23, to be heated, within the heating spaceand carrying the substrate 23 in a direction indicated by an arrow A inthe drawing, a carry-in port 24 for carrying the substrate in theheating space, and a carry-out port 25 for carrying out the substratefrom the heating space.

The heating element 21 is not particularly limited so far as it canrapidly heat the substrate. Heating elements usable herein includeelectrical heating elements and heating elements which burn a gas orother fuel to generate heat. As described above, preferably, the rapidheating is carried out using heating means of which the heating valueper unit area is not less than 120 MJ/m²·hr, more preferably not lessthan 400 MJ/m²·hr. Therefore, preferably, the heating element cangenerate the above heating value. The distance of the surface of thesubstrate from the heating element may be properly determined so that asatisfactory heating value for rapid heating is applied to thesubstrate. The distance would be generally about 5 to 300 mm. Therefore,preferably, the heating element is provided so that the distance betweenthe heating element and the substrate is fixed or variable in the aboverange.

As described above, preferably, the heating temperature is keptsubstantially constant during rapid heating. Therefore, preferably, theheating space of the rapid heating device is satisfactorily insulated byan insulating material 22 and undergoes no significant influence of heatloss from the carry-in port 24 and the carry-out port 25. The carry-inport 24 and the carry-out port 25 may be always in released state asshown in FIG. 5. Alternatively, the carry-in port 24 may be constructedso that the port 24 is usually closed while the port 24 is opened whenthe substrate is carried in the rapid heating device. Likewise, thecarry-out port 25 may be constructed so that the port 25 is usuallyclosed while the port 25 is opened when the substrate is carried outfrom the rapid heating device. The length of the region where thetemperature for rapid heating is kept substantially constant may beproperly determined. The length would be generally 5 cm to 30 m.

The construction of the carrying device 16 is not particularly limitedso far as the device can hold the substrate within the heating space andcan carry through the heating space. The carrying device 16 ispreferably a belt conveyor or a roller conveyor. According to apreferred embodiment of the present invention, in order to attain goodthermal conduction within the heating space, the carrying device 16 isconstructed so that the heating space is not excessively thermallypartitioned. For example, the carrying means is preferably a beltconveyor of a heat-resistant porous belt having a percentage surfaceopening of not less than 20% or a roller conveyor of a group ofheat-resistant rollers. Further, according to another preferredembodiment of the present invention, the carrying means is a beltconveyor of a heat-resistant net having a mesh size up to 50 mm×50 mm ora roller conveyor of a group of continuous heat-resistant rollers havinga pitch of 1 to 300 mm.

The rapidly heated substrate is cooled by the cooling device 10 to roomtemperature. This device is constructed so that when the substrate isplaced in an atmosphere of room temperature, the substrate can be cooledto room temperature. So far as the temperature of the substrate can bedecreased to room temperature, this cooling device may be constructed sothat the substrate simply comes into contact with air of roomtemperature to lower the temperature of the substrate, or alternativelymay be constructed so that air of room temperature or air having atemperature slightly above or below room temperature is forcibly blownagainst the substrate to lower the temperature of the substrate. In thisconnection, it should be noted that rapid cooling has a fear of crackingor the like being created on the surface of the antifouling material.Therefore, preferably, the cooling is carried out at a highest possiblerate with caution so as not to create cracking or other unfavorablephenomenon.

FIG. 6 shows an apparatus provided with a preheating device forpreheating the substrate before coating of the coating composition. Thepreheating device can heat the substrate and raise the temperature ofthe surface of the substrate to a temperature high enough for evenlycoating the coating composition. In the apparatus shown in FIG. 6, apreheating device 11 is provided before the coating device 8. Asdescribed above, preferably, the surface of the substrate is heated bythis preheating device to a temperature of 20 to 400° C. It is a matterof course that an apparatus, shown in FIG. 4, comprising a substratemolding device 5, a grazing device 6, and a firing device 7 may beconnected upstream of the preheating device 11. In this connection,however, since the substrate fired in the firing device 7 still has hightemperature, when the antifouling material is produced continuously fromthe production of a substrate, the provision of this preheating deviceis generally unnecessary. Therefore, the preheating device would begenerally necessary when the substrate has been separately produced andhence does not have satisfactory temperature.

Further, in the apparatus shown in FIG. 6, a drying device 12 for dryingthe substrate coated with the coating composition by means of thecoating device 8 is provided before the rapid heating device 9. Thisdrying device 12 comprises air blowing means or heating means to removeexcess water or solvent component from the surface of the substrate. Inthe apparatus shown in FIG. 6, the rapid heating device 9 and thecooling device 10 may be identical respectively to those shown in FIG.4.

EXAMPLES

The present invention will be described in more detail with reference tothe following examples, though it is not limited to these examples only.

Example A-1

Potassium silicate (0.1% by weight), 0.1% by weight of lithium silicate,and 0.001% by weight of alumina were dispersed in water to prepare acoating composition. The coating composition was spray coated at acoverage of 25 g/m² onto the surface of a glass substrate with thesurface being heated to 100° C. The coated glass substrate was placed ina roller hearth kiln, and heat treated at an atmosphere temperaturewithin the kiln of 350° C. for 30 min. Thus, an inorganic layer wasformed on the glass.

The surface of this inorganic layer had a contact angle thereof withwater of 15 degrees, a contact angle thereof with an oil of 25 degrees,a center line average roughness Ra of 20 nm, a half-value period ofelectrification of 0.3 sec, and a zeta potential at pH 7 of −20 mV. Agreasy contaminant prepared by mixing carbon black with an oil waslinearly dropped on the surface of the glass, and water was then droppedfrom both sides of this line. As a result, this contaminant floated onthe surface of water, and was simply removed from the surface of theglass.

Comparative Example A-1

Heat treatment was carried out in the same manner as in Example 1,except that the inorganic layer was not formed on the surface of theglass substrate. The surface of the treated glass had a contact anglethereof with water of 31 degrees, a contact angle thereof with an oil of22 degrees, a center line average roughness Ra of 2 nm, a half-valueperiod of electrification of 120 sec, and a zeta potential at pH 7 of −2mV. In the same manner as in Example 1, the greasy contaminant preparedby mixing carbon black with an oil was linearly dropped on the surfaceof the glass, and water was then dropped from both sides of this line.As a result, this contaminant strongly adhered onto the surface of theglass, and could not be simply removed from the surface of the glass.

Example A-2

At the outset, ultraviolet light was applied from a BLB lamp to amixture containing a copper-doped alkali dispersion type titanium oxidesol and silver nitrate. Thus, a titanium oxide sol was prepared whereinsilver ions had been supported as a metal by photocatalytic reducingpower. This titanium oxide sol (0.2% by weight) and 0.4% by weight ofpotassium silicate were dispersed in water to prepare a coatingcomposition. The coating composition thus obtained was spray coated at acoverage of 25 g/m² onto the surface of a glazed tile with the surfacebeing heated to 120° C. The coated, glazed tile was rapidly heated at anatmosphere temperature within the furnace of 850° C. for 15 sec. Thus,an inorganic layer was formed on the glazed tile.

The surface of this inorganic layer had a contact angle thereof withwater of 0 degree, a contact angle thereof with an oil of 16 degrees, ahalf-value period of electrification of 0.1 sec, and a zeta potential atpH 7 of −30 mV. A greasy contaminant prepared by mixing carbon blackwith an oil was linearly dropped on the surface of the glazed tile, andwater was then dropped from both sides of this line. As a result, thiscontaminant floated on the surface of water, and was simply removed fromthe surface of the glazed mat tile. Further, the treated, glazed tilehad photocatalytic activity, that is, antimicrobial (bactericidal)activity, antifouling activity, deodorant activity and other degradationactivity. Furthermore, the thin layer formed on the surface of the tilewas a strong layer which had a strength (hardness) of not less than 4 interms of Mohs hardness and possessed excellent abrasion resistance andchemical resistance.

Comparative Example A-2

An inorganic layer was formed on the surface of a glazed tile in thesame manner as in Example A-2, except that the coating composition didnot contain potassium silicate. The inorganic layer thus obtained waseasily separated from the surface of the glazed tile.

Comparative Example A-3

The coating composition as used in Example A-2 was spray coated on thesurface of a glazed mat tile in the same manner as in Example A-2. Thecoated, glazed tile was heat treated within a roller hearth kiln at anatmosphere temperature within the kiln of 800° C. for 60 min. Thus, aninorganic layer was formed on the glazed tile.

The surface of the treated glazed tile had a contact angle thereof withwater of 31 degrees, a contact angle thereof with an oil of 21 degrees,and a half-value period of electrification of 15 sec. The greasycontaminant as used in Example 1 was linearly dropped on the surface ofthe glazed tile, and water was then dropped from both sides of thisline. As a result, this contaminant strongly adhered onto the surface ofthe tile, and could not be simply removed from the surface of the glazedtile.

Example A-3

Potassium silicate (0.2% by weight) and 0.4% by weight of lithiumsilicate were dispersed in water to prepare a coating composition. Thecoating composition was spray coated at a coverage of 25 g/m² onto thesurface of a glass substrate with the surface being heated to 100° C.The coated glass substrate was heat treated within a roller hearth kilnat an atmosphere temperature within the kiln of 350° C. for 30 min.Thus, an inorganic layer was formed on the surface of the glass. Thesurface of the inorganic layer was rubbed 100 times by a hard typeeraser while applying a pressure of 1000 gf/cm². As a result, theinorganic layer remained unchanged and remained strongly adhered ontothe glass substrate.

Comparative Example A-4

An inorganic layer was formed on a glass substrate in the same manner asin Example A-3, except that the atmosphere temperature within the kilnin the heat treatment was changed to 130° C. The surface of theinorganic layer was rubbed 100 times by a hard type eraser whileapplying a pressure of 1000 gf/cm². As a result, the inorganic thinlayer was separated from the glass substrate, demonstrating that theadhesion between the inorganic thin layer and the glass as the substratewas poor.

Separately, an inorganic layer was formed in the same manner as inExample A-3, except that the atmosphere temperature within the kiln inthe heat treatment was changed to 800° C. The surface of the inorganiclayer was rubbed 100 times by a hard type eraser while applying apressure of 1000 gf/cm². As a result, the inorganic thin layer wasseparated from the glass substrate.

Example A-4

An alkali dispersion type titanium oxide sol (0.1% by weight) and 0.4%by weight of lithium silicate were first dispersed in water to prepare acoating composition. The surface of a calcium silicate plate having aninorganic coating was subjected to corona discharge treatment. Thesurface of the treated calcium silicate plate was then heated to 80° C.,and the coating composition was spray coated at a coverage of 25 g/m²onto the surface of the treated calcium silicate plate. The coated,calcium silicate plate was then rapidly heated at an atmospheretemperature within the furnace of 500° C. for 20 sec. Thus, an inorganiclayer was formed on the calcium silicate plate having an inorganiccoating.

The surface of this inorganic layer had a contact angle thereof withwater of 1 degree, a contact angle thereof with an oil of 20 degrees, ahalf-value period of electrification of 0.1 sec, and a zeta potential atpH 7 of −25 mV. A greasy contaminant prepared by mixing carbon blackwith an oil was linearly dropped on the surface of the calcium silicateplate having an inorganic coating, and water was then dropped from bothsides of this line. As a result, this greasy contaminant floated on thesurface of water, and could be simply removed from the surface of thecalcium silicate plate having an inorganic coating. Further, the treatedcalcium silicate plate having an inorganic coating had photocatalyticactivity, that is, antimicrobial activity, antifouling activity,deodorant activity and other degradation activity. Furthermore, theinorganic layer formed on the surface of the calcium silicate platehaving an inorganic coating was a strong layer which had a strength(hardness) of not less than 4 in terms of Mohs hardness and possessedexcellent abrasion resistance and chemical resistance.

Example B-1

(a) Preparation of Coating Composition

At the outset, 5% by weight of lithium silicate (tradename LithiumSilicate 35, manufactured by Nippon Kagaku Kogyo Co., Ltd.) and 0.01% byweight of a surfactant (tradename Emulgen 707, manufactured by KaoCorp.) were dispersed in water to prepare a coating composition.

(b) Preparation of Substrate

In an apparatus shown in FIG. 4, a starting material for ceramic warewas pressed in a forming device 5 to prepare a body. A glaze was thencoated onto the surface of the body in a glazing device 6. Subsequently,the coated body was passed through a roller hearth kiln as a firingdevice 7 kept at a firing temperature of 1150° C. over a period of 40min to perform firing. Thus, a tile was obtained.

(c) Production of Antifouling Material

When the temperature of the tile became 150° C. at the outlet of theroller hearth kiln, the coating composition prepared above was spraycoated onto the surface of the tile. The coverage of the coatingcomposition was 20 g/m². Since the temperature of the tile was as highas 150° C., excess water was instantaneously evaporated. As a result,only solid matter was evenly stacked on the surface of the tile to forman about 0.5 μm-thick thin layer.

The tile was then carried in a furnace as a rapid heating deviceprovided continuously from the firing device 7. The furnace had heatingelements densely arrayed on the upper part of the interior thereof. Thetemperature of the atmosphere in the furnace was about 800 to 1000° C.,the heating value per unit area within the furnace was about 1600MJ/m²·hr, and the heating area was 30 cm×150 cm. The time of residenceof the tile within the furnace was about 30 sec, and the time for whichthe tile had been placed under the heating elements was about 10 sec.The rapid heating permitted the thin layer formed on the surface of thetile to be completely fixed onto the surface of the tile.

The surface of the tile carried out from the furnace had a temperatureincreased to 300 to 350° C. Subsequently, the tile was introduced into acooling device where the tile was sprayed with cold air blown from aboveand below the tile. The tile was cooled to 100-150° C. during the periodof time for which the tile was traveled by 3 m through the coolingdevice.

The tile as an antifouling material thus obtained had high antifoulingactivity against greasy stains or soils and, in addition, had highhydrophilicity. The thin layer formed on the surface of the tile was astrong layer which had a strength (hardness) of not less than 4 in termsof Mohs hardness and possessed excellent abrasion resistance andchemical resistance.

The heat of wetting of the thin layer by water was determined and foundto be as high as 100 erg/cm², suggesting that the thin layer hadsatisfactory hydrophilicity. The heat of wetting is regarded as ameasure of wettability by a solvent, and higher heat of wetting meansthat the wettability by the solvent is higher.

Example B-2

(a) Preparation of Coating Composition

Potassium silicate (tradename Snowtex K, manufactured by Nissan ChemicalIndustry Ltd.) was dispersed in water to prepare a coating compositionhaving a potassium silicate content of 1% by weight. Further, 1 part byweight, based on 100 parts by weight of the potassium silicate sol, of a3% aqueous copper acetate solution was added.

(b) Preparation of Substrate

A large tile (0.9 m×1.8 m) was prepared in the same manner as inExample 1. Specifically, a starting material for ceramic ware wasextruded by means of a forming device 5 in the apparatus shown in FIG. 4to prepare a body. A glaze was then coated onto the surface of the bodyby means of a glazing device 6. The coated body was passed through aroller hearth kiln as a firing device 7 kept at a firing temperature of1150° C. over a period of 3 hr to perform firing. Thus, a large tile wasobtained.

(c) Production of Antifouling Material

When the temperature of the tile became 80° C., the coating compositionwas spray coated onto the surface of the tile as used in Example 1. Thecoverage of the coating composition was 15 g/m². Since the temperatureof the tile was as high as 80° C., excess water was instantaneouslyevaporated. As a result, only solid matter was evenly stacked on thesurface of the tile to form an about 0.2 μm-thick thin layer.

The tile was then carried in a furnace as a rapid heating devicecontinuously provided from the firing device 7. The furnace had heatingelements densely arrayed on the upper part of the interior thereof. Thetemperature of the atmosphere in the furnace was about 800 to 1000° C.,the heating value per unit area within the furnace was about 1600MJ/m²·hr, and the heating area was 1.5 m×28 m. The time of residence ofthe tile within the furnace was about 60 sec, and the time for which thetile had been placed under the heating elements was about 50 sec. Therapid heating permitted the thin layer formed on the surface of the tileto be completely fixed onto the surface of the tile.

The surface of the tile carried out from the furnace had a temperatureincreased to 200 to 250° C. Subsequently, the tile was introduced into acooling device where the tile was sprayed with water. In the coolingdevice, the tile was cooled to 100-150° C. during the period of time forwhich the tile was traveled by 10 m through the cooling device.

The tile as an antifouling material thus obtained had antimicrobialactivity and antialgae activity. Further, the thin layer formed on thesurface of the tile was a strong layer which had a strength (hardness)of not less than 4 in terms of Mohs hardness and possessed excellentabrasion resistance and chemical resistance.

Example B-3

(a) Preparation of Coating Composition

A lithium silicate borate mixed liquid (tradename SLN 55, manufacturedby Nippon Kagaku Kogyo Co., Ltd.) and a cerium oxide sol (tradenameAS-520, manufactured by Taki Chemical Co., Ltd.) were mixed together soas to have a concentration of 0.1% by weight and 0.1% by weight,respective, to prepare a coating composition.

(b) Substrate

A glass plate having a size of 1 m×1 m was provided as a substrate.

(c) Production of Antifouling Material

At the outset, the glass plate was heated to a surface temperature of40° C. by means of a preheating device with the temperature set at 40°C. Thereafter, the coating composition was spray coated on the surfaceof the preheated glass plate. The coverage was 5 g/m². Since thetemperature of the glass substrate was as low as 40° C., the water wereless likely to be evaporated. For this reason, after coating of thecoating composition, the coating was dried at 100° C. The coatingfollowed by drying was repeated three times. This permitted only solidmatter to be evenly stacked on the surface of the glass plate to form anabout 0.1 μm-thick thin layer.

Next, the glass plate with a thin layer formed thereon was carried in afurnace as a rapid heating device provided continuously from thepreheating device. The furnace had heating elements densely arrayed onthe upper part of the interior thereof. The temperature of theatmosphere in the furnace was about 550° C. The time of residence of theglass plate within the furnace was about 2 sec. The rapid heatingpermitted the thin layer formed on the glass substrate to be completelyfixed onto the surface of the glass plate.

The surface of the glass plate carried out from the furnace had atemperature increased to 250 to 350° C. Subsequently, the glass platewith a thin layer fixed thereon was introduced into a cooling devicewhere air was forcibly blown against the glass plate. In the coolingdevice, the glass plate was cooled to 50-150° C. during the period oftime for which the glass plate was traveled by 3 m through the coolingdevice.

The antifouling material thus obtained had high surface smoothness, highultraviolet absorption capacity, and, in addition, excellenthydrophilicity and antifouling properties. Further, the heat of wettingof the thin layer by water was determined and found to be as high as 500erg/cm². The thin layer formed on the surface of the glass plate was astrong layer which had a hardness (Mohs hardness) of not less than 4 andpossessed excellent abrasion resistance and chemical resistance.

Example C-1

An aqueous solution containing 0.5% by weight of potassium silicate wasprepared as a coating composition. The coating composition was spraycoated at a coverage of 25 g/m² onto the surface of a tile with thesurface being heated to 100° C. The coated tile was heat treated withina roller hearth kiln at an atmosphere temperature within the kiln of150° C., 350° C., or 550° C. for 30 min. Thus, inorganic layers wasformed on the surface of the tile. A cylinder having a diameter of 4 cmwas fixed onto the inorganic layers. Distilled water (30 g) wasintroduced into the cylinder, followed by standing at an atmospheretemperature of 50° C. for 2 to 24 hr. 2 hr, 6 hr, and 24 hr after theinitiation of the standing, the amount of potassium eluted wasquantitatively determined by atomic absorption spectroscopy. The resultsof evaluation are shown in FIG. 7.

For the sample which had been heat treated at 150° C., upon immersion ofthe sample in the warm water for 6 hr, potassium contained in the layerwas entirely eluted. In this layer, non-bridging oxygen (particularlysilanol groups (M—OH)) was present in an amount large enough to exhibithydrophilicity. Since the development of a three-dimensional networkstructure of silica was unsatisfactory, the inorganic layer wasconsidered to have somewhat poor abrasion resistance and waterresistance.

For the sample which had been heat treated at 350° C., upon immersion ofthe sample in the warmwater for 6 hr, 30% of potassium contained in thelayer was eluted. In this layer, since the three-dimensional networkstructure of silica was suitably developed, the layer strength was highand the abrasion resistance was excellent. Further, by virtue of thesuitable development of the three-dimensional network structure, a largeamount of non-bridging oxygen (particularly ionically bonded onesM—O—X+) was present in this layer, suggesting that this sample had highhydrophilicity and excellent antifouling properties. That is, thissample had the best balance between the antifouling properties and theabrasion resistance.

For the sample which had been heat treated at 550° C., upon immersion ofthe sample in the warm water for 6 hr, 15% of potassium contained in thelayer was eluted. In this layer, since the three-dimensional networkstructure of silica was sufficiently developed, it is considered thatthe amount of non-bridging oxygen is small although the abrasionresistance and the water resistance are high.

The results of the potassium elution test show the presence of M—O—X+ asnon-bridging oxygen in the inorganic layer. That is, the test resultssuggest that, as compared with the heat treatment at 150° C. and 550°C., the heat treatment at 350° C. creates the presence of a largeramount of non-bridging oxygen (M—O—X+) in the inorganic layer. On theother hand, the mechanical strength of the inorganic layer is increasedin the following order: 150° C.<350° C.<550° C.

Example C-2

The contact angle in water of the inorganic layer with an oil wasmeasured as an index of the releasability of greasy contaminant from theinorganic layer according to the present invention. At the outset, thecoating composition as used in Example C-1 was spray coated at acoverage of 25 g/m² onto the surface of a tile with the surface beingheated to 100° C. The coated tile was heat treated within a rollerhearth kiln at an atmosphere temperature within the kiln of 150° C.,350° C., or 450° C. for 30 min. Thus, inorganic layers was formed on thesurface of the tile. For the inorganic layers, the contact angle inwater thereof with a salad oil, θo(w), was measured.

FIG. 7 schematically illustrate the measurement of the contact angle inwater of the inorganic layer with an oil. As shown in FIG. 7, an oil 36was dropped on an inorganic layer 34 formed on a substrate 33. Theinorganic layer 34 was immersed in water 32 contained in a glasscontainer 31 through a pedestal 35 so that the oil-deposited face faceddownward. At that time, the contact angle of the inorganic layer withthe oil was measured. The contact angle was measured with a contactangle goniometer (CA-X150, manufactured by Kyowa Interface Science Co.,Ltd.). A salad oil as a widely used edible oil, oleic acid contained asa main component in various animal and vegetable oils, and n-octane as ahydrocarbon oil were used as the oil.

Comparative Example C-1

The coating composition as used in Example C-1 was spray coated at acoverage of 25 g/m² onto the surface of a tile with the surface beingheated to 100° C. The coated tile was heat treated within a rollerhearth kiln at an atmosphere temperature within the kiln at 800° C. for30 min. Thus, an inorganic layer was formed on the surface of the tile.For the inorganic layer, the contact angle in water thereof with a saladoil, θo(w), was measured.

Example C-3

Potassium silicate was dried at 100° C. for two days, and thenthermogravimetrically analyzed with TG/DTA 320, manufactured by SeikoInstruments Inc. The measuring temperature ranged from room temperatureto 800° C., and the temperature rise rate was 2° C./min.

The results of Examples C-2 and C-3 and Comparative Example C-1 were asshown in FIG. 9.

For Example C-2, all the samples had a high contact angle in water ofthe inorganic layer with the oil of not less than 120 degrees, that is,had excellent greasy contaminant releasing properties. On the otherhand, for Comparative Example C-1, the sample had a low contact angle inwater of the inorganic layer with the oil of not more than 90 degrees.When the heat treatment temperature exceeded about 500° C., there was arapid degrease in the contact angle in water of the inorganic layer withthe oil. In the case of the inorganic layer in Comparative Example C-1,the greasy contaminant deposited on the inorganic layer could not beremoved simply by washing with water.

The results of the thermogravimetric analysis of potassium silicate inExample C-3 show that, upon a temperature rise in the heat treatmenttemperature, weight reduction occurs in two stages. The weight reductionon the lower temperature side is considered attributable to the removalof physically adsorbed water in potassium silicate, while the weightreduction on the higher temperature side is considered attributable tothe removal of chemical adsorbed water and a structural change. Thestructural change in potassium silicate is considered to be mainlycaused by dehydration as a result of condensation of hydroxyl groupsremaining in the sample. It is expected that the three-dimensionalnetwork structure of silica is developed through the structural change.

The temperature region, in which the contact angle in water of theinorganic layer with the salad oil had been remarkably lowered inExample C-2 and Comparative Example C-1, was in good agreement with theweight reduction temperature on the higher temperature side in thethermogravimetric analysis in Example C-3.

The results of the heat treatment temperature dependency of thethermogravimetric analysis and the contact angle in water of theinorganic layer suggest that the structure of the silica skeleton in thealkali metal silicate contributes greatly to excellent greasycontaminant releasing properties. That is, the inorganic layer accordingto the present invention is considered to develop excellent greasycontaminant releasing properties by synergistic effect of the alkalimetal and the non-bridging oxygen atom.

Example C-4

Coating compositions containing alkali metal silicates according toformulations shown in Table 1 were prepared. The coating compositionswere spray coated at a coverage of 25 g/m² onto the surface of atableware with the surface being heated to 100° C. The coated tablewarewas heat treated within a roller hearth kiln at an atmospheretemperature within the kiln of 350° C. for 30 min. Thus, inorganiclayers were formed on the surface of the tableware.

Before and after the immersion of the samples in warm water of 50° C.for 6 hr, the samples were evaluated for the releasability of the greasycontaminant on the inorganic layers. The immersion in warm watercorresponds to the inorganic layers after repeated washing. For theinorganic layer samples, the contact angle in water of the inorganiclayer with a salad oil (θo(w)) before and after the immersion of thesamples in warm water of 50° C. for 6 hr and the contact angle in air ofthe inorganic layer with water (θw) and the contact angle in air of theinorganic layer with a salad oil (θo) before the immersion in warm waterwere measured.

A greasy stain releasing test was carried out as follows. An oil wasapplied in an area of 5 cm×5 cm on the inorganic layer formed on thesurface of the substrate. The sample was then slanted by 45 degrees,and, in this state, running water was flowed at a rate of 2400 g/minfrom above the oil-coated face. This oil staining-water washing cyclewas repeated five times. After the repetition of the greasy stainreleasing test five times, the level of the oil remaining on the surfaceof the inorganic layer was determined, and the results were reduced tofour evaluation grades A to D with A being the best. When no greasystain was observed on the surface of the inorganic layer upon washingwith water in an amount of less than 100 cc after the fivestaining-washing cycles, the greasy stain releasing property wasrevaluated as “A”; when no greasy stain was observed on the surface ofthe inorganic layer upon washing with water in an amount of not lessthan 100 cc after the five staining-washing cycles, the greasy stainreleasing property was revaluated as “B”; when a small amount of thegreasy stain remaining removed from the surface of the inorganic layerafter the five staining-washing cycles was removed and becameunnoticeable upon wiping off with a sponge in combination with waterwashing, the greasy stain releasing property was revaluated as “C”; andwhen the greasy stain on the inorganic layer substantially entirelyremained unremoved after the five staining-washing cycles and could notbe removed without use of a neutral detergent, the greasy stainreleasing property was evaluated as “D.” A salad oil as a widely usededible oil, oleic acid contained as a main component in various animaland vegetable oils, or n-octane as a mineral oil (hydrocarbon) were usedas the oil.

TABLE 1 Material(s) Sample contained SiO₂, K₂O, Li₂O, Firing No. inaqueous solution wt % wt % wt % temp., ° C. 1 Potassium silicate 0.5    0.2     0    350 2 Lithium silicate A 0.5     0      0.075 350 3 Lithiumsilicate B 0.5     0      0.041 350 4 Potassium silicate + 0.25 + 0.1 + 0 +   350 Lithium silicate A 0.25 + 0       0.0375 5 Potassiumsilicate + 0.32 + 0.13 + 0 +   350 Silica sol 0.18    0      0   

Example C-5

Potassium silicate having a composition shown in Table 2 and a titaniumoxide (anatase form) sol were dispersed in water to prepare coatingcompositions. The coating compositions were spray coated at a coverageof 25 g/m² onto the surface of a tile with the surface being heated to100° C. The coated tile was heat treated within a roller hearth kiln atan atmosphere temperature within the kiln of 350° C. for 30 min. Thus,inorganic layers was formed on the surface of the tile.

These inorganic layers were evaluated in the same manner as in ExampleC-4. Titanium oxide is known to be an oxide semiconductor havingphotocatalytic activity and to exhibit superhydrophilification abilityand strong oxidizing power upon photoexcitation. Therefore, titaniumoxide can provide excellent antifouling properties under an environmentexposed to sunlight. In this example, the sample was evaluated withoutlight irradiation for the excitation of titanium oxide. Thisexperimental condition was used in order to demonstrate that, even inthe case where sufficient light is not present under a daily lifeenvironment, the inorganic layer has excellent greasy stain releasingproperties.

TABLE 2 Sample Material(s) contained SiO₂, K₂O, Li₂O, Firing No. inaqueous solution wt % wt % wt % temp., ° C. 6 Potassium silicate 0.5 0.20    550 7 Lithium silicate A 0.5 0   0.075 550 8 Lithium silicate B 0.50   0.041 550

Example C-6

Alkali metal silicates having compositions shown in Table 3 weredispersed in water to prepare coating compositions. The coatingcompositions were spray coated at a coverage of 25 g/m² onto the surfaceof a tile with the surface being heated to 100° C. The coated tile wasrapidly heat treated at an atmosphere temperature within the furnace of850° C. for 15 sec. Thus, inorganic layers was formed on the surface ofthe tile. These inorganic layers were evaluated in the same manner as inExample C-4.

TABLE 3 Sample Material(s) contained SiO₂, K₂O, Ti₂O, Firing No. indispersion wt % wt % wt % temp., ° C.  9 Potassium silicate + 0.4 0.160.1 350 Titanium oxide sol 10 Potassium silicate + 0.3 0.12 0.2 350Titanium oxide sol 11 Potassium silicate + 0.1 0.04 0.4 350 Titaniumoxide sol

Comparative Example C-2

Alkali metal silicates having compositions shown in Table 4 weredispersed in water to prepare coating compositions. The coatingcompositions were spray coated at a coverage of 25 g/m² onto the surfaceof a tile with the surface being heated to 100° C. The coated tile washeat treated within a roller hearth kiln at an atmosphere temperaturewithin the kiln of 800° C. for 30 min. Thus, inorganic layers was formedon the surface of the tile. These inorganic layers were evaluated in thesame manner as in Example C-4.

TABLE 4 Sample Evaluation result on No. θo(w), ° θw, ° θo, °releasability of greasy stain  1 160.8 0 22.3 A  2 159.9 2.1 25.4 A  3166.5 2.3 26 A  4 160.2 4.1 22.7 A  5 160   0 25.8 A  6  83.8 9.9 24.5 D 7  91.5 22.6 28.4 D  8  83.3 22.1 28.1 D  9 159.2 1.6 10 A 10 151.2 010.3 A 11 31  0 8.2 D Untreated 115   18 20.5 C tile

Comparative Example C-3

An untreated tile having no inorganic layer on its surface was evaluatedin the same manner as in Example C-4.

The results of the evaluation for Examples C-4, C-5, and C-6 andComparative Examples C-2 and C-3 were as shown in Table 5.

TABLE 5 Sample Evaluation result on No. θo(w), ° θw, ° θo, °releasability of greasy stain  1 160.8 0 22.3 A  2 159.9 2.1 25.4 A  3166.5 2.3 26 A  4 160.2 4.1 22.7 A  5 160   0 25.8 A  6  83.8 9.9 24.5 D 7  91.5 22.6 28.4 D  8  83.3 22.1 28.1 D  9 159.2 1.6 10 A 10 151.2 010.3 A 11 31  0 8.2 D Untreated 115   18 20.5 C tile

Example C-7

Alkali metal silicates having compositions shown in Table 6 weredispersed in water to prepare coating compositions. The coatingcompositions were spray coated at a coverage of 25 g/m² onto the surfaceof a tile with the surface being heated to 100° C. The coated tile washeat treated within a roller hearth kiln at an atmosphere temperaturewithin the kiln of 350° C. for 30 min. Thus, inorganic layers wereformed on the surface of the tile. For these inorganic layers, beforeand after immersion in warm water of 50° C. for 6 hr, the contact anglein water thereof with oleic acid and the contact angle in water thereofwith n-octane were measured. Further, these inorganic layers wereevaluated for the releasability of oleic acid and n-octane as greasystains.

TABLE 6 Material(s) Heat Sample contained in SiO₂, K₂O, Li₂O, treatmentNo. aqueous solution wt % wt % wt % conditions 14 Lithium silicate 0.5    0      0.075 350° C. × 30 min 15 Lithium silicate 0.5     0     0.041 350° C. × 30 min 16 Lithium silicate + 0.25 + 0.1 + 0 +    350° C.× 30 min Potassium silicate 0.25    0      0.02 

The results of Example C-7 were as shown in Table 7.

TABLE 7 Releasability of Sample greasy stain θo(w), ° No. Oleic acidn-Octane Oleic acid n-Octane Before immersion in warm water of 50° C.for 6 hr Ex. C-7 14 B A 146.9 160.2 15 A B 165.8 159.8 16 A A 163.7161.2 After immersion in warm water of 50° C. for 6 hr Ex. C-7 14 C C119.4 121.7 15 A B 150.8 134.4 16 B B 143.2 131.5

Example C-8

Various alkali metal silicates having compositions shown in Table 8either alone or in combination with TiO₂ were dispersed in water toprepare coating compositions. In this case, SLN 73 manufactured byNippon Kagaku Kogyo Co., Ltd. was also used as an alkali metal silicatecontaining a plurality of alkali metal species and, in addition, boron.These coating compositions were spray coated at a coverage of 25 g/m²onto the surface of a tile with the surface being heated to 100° C. Thecoated tile was heat treated within a roller hearth kiln at anatmosphere temperature within the kiln of 350° C. for 30 min. Thus,inorganic layers were formed on the surface of the tile.

For these inorganic layers, before and after immersion in warm water of50° C. for 6 hr, the contact angle in water thereof with a salad oil(θo(w)) was measured. Further, these inorganic layers were evaluated forthe releasability of a salad oil as a greasy stain. Further, theinorganic layers were evaluated for the layer strength by performing asliding test before and after the immersion in warm water. In thesliding test, the inorganic layers were rubbed 100 times by a hard typeeraser while applying a pressure of as 1000 gf/cm², followed byinspection of the surface state of the inorganic layers. The resultswere reduced to evaluation grades A to D.

When the inorganic layer surface substantially remained unchanged andretained a very good state, the layer strength was evaluated as “A”;when the inorganic layer surface underwent a slight change but stillretained a good state, the layer strength was evaluated as “B”; when apart of the surface of the inorganic layer was damaged, the layerstrength was evaluated as “C”; and when the surface of the inorganiclayer was significantly damaged, the layer strength was evaluated as“D.”

TABLE 8 Sample Material(s) contained in SiO₂, Li₂O, K₂O, Na₂O, B₂O₃,TiO₂, Heat treatment No. aqueous solution wt % wt % wt % wt % wt % wt %conditions 17 Potassium silicate 0.5 0 0.2 0 0 0 350° C. × 30 min 18Potassium silicate + 0.25 + 0 + 0.1 + 0 0 0 350° C. × 30 min Lithiumsilicate 0.25 0.0375 0 19 SLN 73 0.5 0.043 0 0.063 0.008 0 350° C. × 30min 20 SLN 73 + 0.5 0.043 0 0.063 0.008 0.1 350° C. × 30 min Titaniumoxide sol

The results of Example C-8 are summarized in Table 9.

TABLE 9 Before immersion in warm water of 50° C. for After immersion inwarm water of 50° C. for 6 hr 6 hr Layer Releasability of LayerReleasability of Sample No. strength θo(w),° greasy stain strengthθo(w),° greasy stain Example 17 B 160.8 A D 136 B C-8 18 B 160.2 A C146.8 A 19 B 151.2 A B 136.5 B 20 B 161.3 A B 140 A

Example D-1

An alkali silicate (Lithium Silicate 35, manufactured by Nissan ChemicalIndustry Ltd.) (3% by weight) was dispersed in water to prepare acoating composition. The coating composition was spray coated onto thesurface of a glazed tile having a size of 15 cm square (AB02E01,manufactured by TOTO, LTD.). The coated tile was fired at an atmospheretemperature of 850° C. for 10 sec to bring the surface temperature ofthe substrate to 300° C. At that time, the presence of zircon andunmelted silica particles in the glass layer on the surface of theglazed tile was confirmed by EPMA. A layer of lithium silicate wasformed there on to prepare a sample with an inorganic layer formedthereon. The layer thickness was 3 μm.

Immediately after firing, the contact angle of the sample with water wasmeasured with a contact angle goniometer (Model CA-X150, manufactured byKyowa Interface Science Co., Ltd.; detection limit on low angle side: 1degree), and found to be 5 degrees. The contact angle was measured 30sec after dropping of a water droplet through a microsyringe on thesurface of the sample. The sample was allowed to stand in a dark placefor one week, followed by the measurement of the contact angle. As aresult, the contact angle of the sample with water remained unchangedand was 5 degrees. Next, one drop of a salad oil was put on this tileand, the tile was then immersed in water. Thirty sec after theinitiation of immersion, the contact angle in water of the sample withthe oil was measured. As a result, the reading of the contact anglegoniometer was 140 degrees, indicating that the surface of the samplewas oil repellent in water. Further, the sample had a zeta potential atpH 7 of −20 mV and a half-value period of electrification of 8 sec.

Example D-2

An alkali silicate (Potassium Silicate 1K, manufactured by Nippon KagakuKogyo Co., Ltd.) (0.2%by weight), 0.1% by weight of a silica sol(Snowtex O, manufactured by Nissan Chemical Industry Ltd.), and 0.001%by weight of an alumina sol (AS 520, manufactured by Nissan ChemicalIndustry Ltd.) were dispersed in water to prepare a coating composition.The coating composition was spray coated onto the surface of a glazedtile having a size of 15 cm square (AB02E01). The coated tile was firedat a temperature of 400° C. for 40 min. Thus, a sample with an alkalisilicate layer being formed thereon was obtained.

At that time, the presence of zircon and unmelted silica particles inthe glass layer on the surface of the glazed tile was confirmed by EPMA.The layer thickness was 0.2 μm. The glossiness of the tile was 50.Immediately after firing, the contact angle of the sample with water wasmeasured, and found to be 0 degree. The sample was allowed to stand in adark place for two weeks, followed by the measurement of the contactangle thereof with water. As a result, the contact angle was 3 degrees.Further, the contact angle in water of the sample with a salad oil was120 degrees. The sample had a half-value period of electrification of 7sec and a surface roughness of Ra=25 nm and Sm=200 nm.

Example D-3

An alkali silicate (Lithium Silicate 35, manufactured by Nissan ChemicalIndustry Ltd.) (1% by weight), 0.5% by weight of a silica sol (SnowtexOUP, manufactured by Nissan Chemical Industry Ltd.), and 0.001% byweight of a titania sol (A-6, manufactured by Taki Chemical Co., Ltd.)were dispersed in water to prepare a coating composition. The coatingcomposition was spray coated onto the surface of a glazed tile having asize of 15 cm square (AB02E01). The coated tile was fired at atemperature of 250° C. for 10 min. Thus, a sample with an alkalisilicate-containing layer being formed thereon was obtained.

At that time, the presence of zircon particles in the glass layer on thesurface of the glazed tile was confirmed by EPMA. The layer thicknesswas 0.2 μm. The glossiness of the tile was 70. Immediately after firing,the contact angle of the sample with water was measured, and found to be0 degree. The sample was allowed to stand in a dark place for two weeks,followed by the measurement of the contact angle thereof with water. Asa result, the contact angle was 3 degrees. Further, the contact angle inwater of the sample with a salad oil was 120 degrees.

Evaluation Test on Exhaust Gas Contaminant Releasing Property

Each of the samples prepared in the examples was tested for theevaluation of exhaust gas contaminant releasing properties according tothe following procedure.

At the outset, the initial diffuse reflectance of the surface of thesample was measured with a potable reflectiometer (tradename: ModelPG-3D, manufactured by Nippon Denshoku Co., Ltd.). The sample was placedwithin a container connected directly to an exhaust pipe of a dieselcar, and an exhaust gas was introduced into the container. In this case,the exhaust gas was introduced until the color difference on the surfaceof the sample reached about 20 or until the diffuse reflectance reachednot more than 55%. Thus, the exhaust gas was forcibly deposited onto thesurface of the sample. In this case, the engine speed was about 3000rpm, and the time required for the deposition was about 10 min.

Next, the tile was washed by water spraying. In this case, running waterof room temperature was sprayed as washing water against the surface ofthe tile at a flow rate of about 400 cc/m² and a water pressure of about0.6 kgf/cm².

For the samples after washing, the diffuse reflectance and therestoration of the diffuse reflectance, and the color difference weremeasured.

All the samples prepared in the examples of the present invention didsatisfy requirements, that is, a diffuse reflectance after washing ofnot less than 60%, a restoration of the diffuse reflectance of not lessthan 75%, and a color difference of not more than 5. Also after therepetition of contamination-washing cycle three times, these samplessatisfied the requirements. This indicates that the antifoulingmaterials according to the present invention have excellent antifoulingproperties.

According to the present invention, the antifouling requirements aremore preferably such that the diffuse reflectance after washing is notless than 70%, the restoration of the diffuse reflectance is not lessthan 90% and the color difference is not more than 2. Some of the abovesamples satisfied also the more preferred requirements.

What is claimed is:
 1. An antifouling material comprising: a substrate;and an inorganic layer which is mainly composed of an alkali silicate,said inorganic layer being fixed as the outermost layer of theantifouling material; the content of alkali metal in the inorganic layerbeing not less than 10% by weight as measured by X-ray photoelectronspectroscopy from the surface layer side and non-bridging oxygen beingpresent in an amount satisfying an alkali metal elution from theinorganic layer of 0.001 to 80%, the inorganic layer having a surfacewhich has a center line average roughness (Ra) of Ra<500 nm and having athickness of not more than 5 μm, said inorganic layer containing thealkali metal and the non-bridging oxygen in an amount effective toremove contaminants, derived from an exhaust gas, adhered on the surfaceof the inorganic layer with running water alone to restore diffusereflectance of the surface to not less than 75% of initial diffusereflectance.
 2. The and fouling material according to claim 1, whereinthe restoration of the diffuse reflectance is not less than 80%.
 3. Theantifouling material according to claim 1, wherein the restoration ofthe diffuse reflectance is not less than 90%.
 4. The antifoulingmaterial according to claim 1, wherein the concentration of the alkalimetal in the inorganic layer is higher than the concentration of thealkali metal in the substrate.
 5. The antifouling material according toclaim 1, wherein the contact angle in water of the inorganic layer witholeic acid is not less than 100 degrees.
 6. The antifouling materialaccording to claim 5, wherein the contact angle is more than 120degrees.
 7. The antifouling material according to claim 6, wherein thecontact angle is more than 140 degrees.
 8. The antifouling materialaccording to claim 1, wherein, after immersion of the antifoulingmaterial in warm water of 50° C. for 6 hr, the contact angle in water ofthe surface of the inorganic layer with oleic acid is more than 120degrees.
 9. The antifouling material according to claim 1, wherein theheat of immersion of the inorganic layer on an oil is smaller than thaton water.
 10. The antifouling material according to claim 1, wherein theinorganic layer has a thickness of 0.01 to 5 μm.
 11. The antifoulingmaterial according to claim 1, wherein the center line average roughness(Ra) is Ra<100 μm.
 12. The antifouling material according to claim 1,wherein the surface of the inorganic layer has a half-value period ofelectrification of not more than 10 sec.
 13. The antifouling materialaccording to claim 1, wherein the inorganic layer, when immersed inwater having pH 7, has a negative zeta potential.
 14. The antifoulingmaterial according to claim 1, wherein the surface of the inorganiclayer has a pH exceeding
 7. 15. The antifouling material according toclaim 1, further comprising an amorphous metal oxide selected from thegroup consisting of Al₂O₃, ZrO₂, B₂O₃, and P₂O₅.
 16. The antifoulingmaterial according to claim 1, wherein the alkali metal is at least onemember selected from the group consisting of lithium, sodium, andpotassium.
 17. The antifouling material according to claim 1, whereinthe inorganic layer contains an antimicrobial agent.
 18. The antifoulingmaterial according to claim 1, wherein the substrate comprises: a body;and a particulate material containing glaze layer and/or a transparentthin layer provided on the body.
 19. The antifouling material accordingto claim 1, wherein the substrate contains a particulate material in itssurface.
 20. The antifouling material according to claim 1, wherein theparticulate material is at least one element selected from the groupconsisting of silicon, aluminum, iron, titanium, magnesium, calcium,zirconium, zinc, cobalt, manganese, chromium, copper, silver, lead, andnickel.
 21. The antifouling material according to claim 1, wherein theinorganic layer further contains a photocatalytically active metaloxide, part of which is exposed on the surface of the inorganic layer.22. The antifouling material according to claim 1, wherein the substratecomprises at least one member selected from the group consisting ofceramics including tiles, sanitary wares, tablewares, ceramicwhitewares, glass, natural stone, cement, concrete, metals, fibers, andplastics, or a laminate of these substrates.
 23. The antifoulingmaterial according to claim 1, wherein the inorganic layer is formed asa stacked or multi-layered coating.